The high-resolution infrared spectrum of the ν3 + ν8 combination band of jet-cooled propyne

The high-resolution infrared spectrum of the ν3 + ν8 combination band of propyne (CH3CCH) is presented for the first time. Continuous-wave cavity ring-down spectroscopy is used to measure this weak infrared band in the 3175 cm−1 region using a supersonic free jet. The rotational analysis of the experimental spectrum results in accurate spectroscopic parameters for the ν3 + ν8 combination vibrational state. Severe perturbations are found for K = 3 and 4 rotational levels that are likely due to near-resonant or non-resonant interactions between the ν3 + ν8 and other vibrational states. Moreover three parallel-transition type subbands are observed and their analysis is presented as well.